The present invention relates generally to controlling a reactant gas in a vehicle fuel cell system, and more particularly to devices and methods for controlling the gas by regulating a backpressure valve and a bypass valve connected to a fuel cell stack.
Fuel cells convert a fuel into usable electricity via chemical reaction. A significant benefit to such an energy-producing means is that it is achieved without reliance upon combustion as an intermediate step. As such, fuel cells have several environmental advantages over internal combustion engines (ICEs) and related power-generating sources. In a typical fuel cell—such as a proton exchange membrane or polymer electrolyte membrane (in either event, PEM) fuel cell—a pair of catalyzed electrodes are separated by an ion-transmissive medium (such as Nafion™). The chemical reaction occurs when a gaseous reducing agent (such as hydrogen, H2) is introduced to and ionized at the anode and then made to pass through the ion-transmissive medium such that it combines with an ionized form of a gaseous oxidizing agent (such as oxygen, O2) that has been introduced through the other electrode (the cathode); this combination of ionized reactants (along with electrons that have passed through the load) form water as a byproduct. The electrons that were liberated in the ionization of the hydrogen proceed in the form of direct current (DC) to the cathode via external circuit that typically includes a load where useful work may be performed. The power generation produced by this flow of DC electricity can be increased by combining numerous such cells to form a fuel cell stack.
To improve the delivery of the reactant gases, pressurized sources are often used. For example, the air being delivered to the cathode side of a fuel cell system is often by way of a compressor, where ancillary equipment—such as valves, controllers or the like—is used to regulate the airflow between the compressor and fuel cell. An inherent attribute of a compressor-aided delivery system (at least as it relates to cathode-side operation) is that the cathode's pressure and flow control are coupled together; this coupling means that stable operation can often be best achieved through a feedforward-based control strategy to take advantage of known or ascertainable mathematical relationships. In this way, a command signal based on known operational characteristics of the compressor may be sent to the compressor to affect a change therein in a way that will ensure predictable, repeatable response.
Nevertheless, it remains challenging and difficult to develop new control systems to precisely regulate the flow of such reactants used in a fuel cell system. This is particularly acute in vehicular-based fuel cell systems where reliability, weight and cost further compound the challenges.